I need some advice. I have my Macbook running MacOS High Sierra Version 10.13 Beta. I'd like to downgrade to MacOS Sierra, can someone please help me with resources, a link, or anything similar?
Unfortunately, there's no simple 'Revert' option. You cannot go 'downhill' even using Time Machine, unless you swapped out your Time Machine drive right before the update - it simply won't let you.
Your only option is from the App Store, using your Purchase History to find the previous OS installer; download, make a bootable USB key & start afresh from there. iCloud ought to be able to sync, & you will be able to use Time Machine to pull some data back, but it will not be seamless.
As a cautionary tale, I'll link to my trials & tribulations trying to revert from Sierra to El Capitan, which even with multiple backups wasn't painless - Revert to El Capitan